The present invention relates to a computer process for determining planes in a 3-dimensional space using individual data points and more specifically to such a process for performing structural geologic analysis on topographical data.
It has been long known by earth scientists that many physiographic relief forms, such as stream valleys, mountain escarpments and the like, are controlled by the underlying geologic structure of the area. Geologic structures, for example bedding and fracture planes and geologic faults, affect the differential erosion of the surface materials. original work in this field of study was performed by W. H. Hobbs and described by him in "Lineaments of the Atlantic Border Region", Bull. Geol. Soc. Am., Vol. 15, 1903. The term "lineament" is therein defined as any mappable, single or composite linear feature of the surface, whose parts are aligned in a rectilinear or sligntly curvilinear relationship and which differs distinctly from the patterns of adjacent features and presumably reflects a subsurface phenomenon. Since this original work, over two thousand lineament studies have been published.
Studies by early structural geologists were limited by the availability of high quality topographic maps and their abiltiy to gain synoptic views of large areas of the earth. Aerial photography, imaging from rockets and more recently remote imaging from satellite systems now provide an overwhelmingly large database for structural geologic analysis.
However, assessment of local structural features, such as the orientation of jointing patterns, faults, and the like, are often found to be highly dependent on the interpreter. Studies have shown that significant variations in interpretation can be expected from several photo analysts using the same imagery. These studies utilizing various data sets, such as aerial and satellite photography, imagery from optical mechanical imaging systems, imaging radar data and photos of low angle illuminated plastic relief maps, indicate that all of these types of data contain a bias which is related to the illumination angle. Shadow enhancement tends to accent lineaments at approximately 30 degrees on either side of the illumination angle and suppress lineaments on the axis of the illumination. Similar effects have been observed in box filtered digital data and by the applicant in lineament studies utilizing digital shaded topography.
It is therefore desirable to establish a quantitative link between topographic relief patterns and geologic structures where the bias of the interpreter is substantially reduced or eliminated.